The government wants major new buildings to be designed with panic rooms, truck-bomb barriers and limited glazing to counter terrorist attacks in a policy which architects have warned could blight the attractiveness of towns and cities.

Home Office counter-terrorism experts will this summer begin training designers to reduce the carnage caused by suicide and vehicle bombs detonated in crowded places such as shopping centres.

A training video and draft advice, seen by the Guardian, urges architects to design each window to be no larger than three square metres and to avoid using masonry cladding on any building higher than two storeys. The tactics are aimed at stopping flying stone and shards of glass doubling the deadly impact of a bomb.

Concrete and steel blockades should be built outside buildings to block vehicle-borne bombs such as the one used in the attack on Glasgow airport last summer. And buildings should be set back from the road by 50 metres to foil attacks such as the failed attempt to blow up the Tiger Tiger bar in central London.

The training workshops are part of the government's national security strategy outlined by Gordon Brown last week. The prime minister promised to "work with architects and planners to 'design in' safe areas, and blast-resistant materials and enhanced physical protection against vehicle bomb attacks".

Senior officials said the measures were needed because of the increased risk that terror tactics seen in Iraq and Afghanistan are being tried in Britain. But the result could be an "inhuman" urban landscape which fosters division and paranoia, according to leading designers.

"This sounds absolutely idiotic," said Piers Gough, an architect and commissioner of the Commission for Architecture and the Built Environment. "The whole thrust of our public realm strategy is to get rid of barriers in our streets. Barriers are essentially inhuman and suggest segregation and that's the last thing we want to introduce into the city. We used to be afraid of cars but now it seems to be terrorism. It seems like another way of stopping us living a civilised life."

He warned that the National Counter Terrorism Security Office's (NaCTSO) advice to set buildings back from potential attack points would strip designers of the ability to create a compact city.

It would also mean that landmark proposals which already have permission, such as the 66-storey tower at London Bridge designed by Renzo Piano, will be at odds with government advice. Piano's design is fully glazed and has been nicknamed "the shard of glass".

Public buildings which incorporate defences against truck bombs, such as the black steel barriers alongside the Houses of Parliament, have drawn criticism for their ugliness. The Home Office cites Arsenal's use of concrete letters spelling out its club name at its recently built football stadium as a good example of elegant counter-terror design.

"It is a national programme attempting to train all the key designers of major public projects," said Carl Whitley-Jones, the NaCTSO officer in charge of the programme. "The theatre [of terrorism] has changed. Now the target is crowded places and mass casualties.

"We are asking architects to come up with designs that make these places safe, but won't repel [people] from wanting to come out and enjoy themselves."

Police officers who advise planning authorities on the security of proposed buildings will be trained and the government's design watchdog, which is vetting designs for the Olympics, will be urged to incorporate the advice in its scrutiny of the country's biggest building proposals.

Other advice includes avoiding parking close to or inside buildings. Secure spaces within buildings - 0.66 square metres per occupant, the advice suggests - should be built so people do not flee one blast only to run into the path of another.

The training video shows what happens when a fictional city square lined with shops and offices is attacked by two suicide bombers and a truck bomb.

A voiceover intones: "We know that right now our public places are under surveillance from individuals who are trained to look for vulnerability. The truth is some structures and spaces can actually assist in their appalling ambition ... Maybe you can't see the responsibility you have got. Until you do we are back to where we started, back to anxiety, back to fear."

Adrian Burton, of Broadway Malyan Architects, who attended a pilot course, said: "While a lot of people agree with this advice, it won't happen unless it is enforced with legislation. We would like to see counter-terrorism building regulations so every developer is on a level playing field."